The present invention relates to heat sensitive recording materials. It more particularly relates to such recording material in the form of a supporting substrate, for example, a paper sheet, synthetic paper sheet or plastic resin film coated with colour-forming systems comprising a colorless or pale coloured electron donative compound (colour forming compound) and an organic electron acceptor (developer).
Heat sensitive recording has conventionally been used as a system for recording transferred information through the mediation of heat, by utilising a colour reaction between a colour forming compound and a developer.
The properties which are most desirable in a colour forming material, in addition to the effective development of colour, are thermal response, background whiteness and image stability, especially light fastness of the developed colour, heat and moisture fastness of the developed colour, oil fastness of the developed colour, plasticiser resistance of the developed colour and water fastness of the developed colour.
A need exists to improve the above properties and to improve the archival capabilities of such recording materials. It is an object of the present invention to provide heat sensitive recording materials with improved properties, especially to provide an increase in image stability whilst improving the background whiteness of the paper before imaging and the background whiteness of the undeveloped portion after imaging.
The present invention is directed to a heat sensitive recording material, comprising
a) at least one colour forming compound, and
b) at least one developer of the formula 
xe2x80x83wherein
R1 is unsubstituted or substituted phenyl, naphthyl or C1-C20alkyl,
X is a group of the formula 
A is unsubstituted or substituted phenylene, naphthylene or C1-C12alkylene, or is an unsubstituted or substituted heterocyclic group,
B is a linking group of formula xe2x80x94Oxe2x80x94SO2xe2x80x94, xe2x80x94SO2xe2x80x94Oxe2x80x94, xe2x80x94NHxe2x80x94SO2xe2x80x94, xe2x80x94SO2xe2x80x94NHxe2x80x94, xe2x80x94Sxe2x80x94SO2xe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94NHxe2x80x94, xe2x80x94NHxe2x80x94COxe2x80x94, xe2x80x94NHxe2x80x94COxe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94COxe2x80x94NHxe2x80x94, xe2x80x94Sxe2x80x94CSxe2x80x94NHxe2x80x94, xe2x80x94COxe2x80x94NHxe2x80x94SO2xe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94NHxe2x80x94SO2xe2x80x94, xe2x80x94NHxe2x95x90CHxe2x80x94, xe2x80x94COxe2x80x94NHxe2x80x94COxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94SO2xe2x80x94NHxe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94Oxe2x80x94 and xe2x80x94Oxe2x80x94POxe2x80x94(OR2)2, and
R2 is unsubstituted or substituted aryl or benzyl or C1-C20alkyl,
with the proviso, that, if B is not a linking group of formula xe2x80x94Oxe2x80x94SO2xe2x80x94, R2 is unsubstituted or substituted phenyl, naphthyl or C1-C8alkyl and that, if B is xe2x80x94Oxe2x80x94, R2 is not alkyl.
R1 as phenyl or naphthyl can be unsubstituted or substituted by, for example, C1-C8alkyl, C1-C8alkoxy or halogen. Preferred substituents are C1-C4alkyl, especially methyl or ethyl, C1-C4alkoxy, especially methoxy or ethoxy, or halogen, especially chlorine. R1 as naphthyl is preferably unsubstituted. R1 as phenyl is preferably substituted, especially by one of the above alkyl substituents.
R1 as C1-C20alkyl can be unsubstituted or substituted by, for example C1-C8alkoxy or halogen. Preferred substituents are C1-C4alkoxy, especially methoxy or ethoxy, or halogen, especially chlorine. R1 as C1-C20alkyl is preferably unsubstituted.
Preferably, R1 is phenyl which is unsubstituted or substituted by C1-C8alkyl, C1-C8alkoxy or halogen. Of most importance are the substituted phenyl groups. Highly preferred are phenyl groups which are substituted by C1-C4alkyl, preferably by methyl.
X is preferably a group of the formula 
especially a group of the formula 
A as a phenylene or naphthylene group can be unsubstituted or substituted by, for example, C1-C8alkyl, halogen-substituted C1-C8alkyl, C1-C8alkoxy-substituted C1-C8alkyl, C1-C8alkoxy, halogen-substituted C1-C8alkoxy, C1-C8alkylsulphonyl, halogen, phenyl, phenoxy or phenoxycarbonyl. Preferred alkyl and alkoxy substituents are those containing 1 to 4 carbon atoms. Preferred substituents are C1-C8alkyl, halogen-substituted C1-C8alkyl, C1-C8alkyl-sulphonyl or halogen. A as a naphthylene group is preferably unsubstituted.
A as a heterocyclic group is preferably pyrimidylene which is unsubstituted or substituted by C1-C8alkyl, especially by C1-C4alkyl.
A as a C1-C12alkylene group is preferably C1-C8alkylene, especially C1-C4alkylene.
Preferred groups A are phenylene groups which are unsubstituted or substituted by C1-C8alkyl, halogen-substituted C1-C8alkyl, C1-C8alkoxy-substituted C1-C8alkyl, C1-C8alkoxy, halogen-substituted C1-C8alkoxy, C1-C8alkylsulphonyl, halogen, phenyl, phenoxy or phenoxycarbonyl, especially C1-C8alkyl, halogen-substituted C1-C8alkyl, C1-C8alkylsulphonyl or halogen.
Highly preferred groups A are phenylene groups which are unsubstituted or substituted by C1-C4alkyl or halogen, especially unsubstituted phenylene groups.
Preferred linking groups B are those of formulae xe2x80x94Oxe2x80x94SO2xe2x80x94, xe2x80x94SO2xe2x80x94Oxe2x80x94, xe2x80x94SO2xe2x80x94NHxe2x80x94, xe2x80x94Sxe2x80x94SO2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94 and xe2x80x94Oxe2x80x94COxe2x80x94NHxe2x80x94, especially linking groups of formulae xe2x80x94Oxe2x80x94SO2xe2x80x94, xe2x80x94SO2xe2x80x94Oxe2x80x94 and xe2x80x94SO2xe2x80x94NHxe2x80x94. Highly preferred are the linking groups B of formula xe2x80x94Oxe2x80x94SO2xe2x80x94 and xe2x80x94Oxe2x80x94.
R2 as aryl is preferably phenyl or naphthyl which can be unsubstituted or substituted by, for example, C1-C8alkyl, halogen-substituted C1-C8alkyl, C1-C8alkoxy-substituted C1-C8alkyl, C1-C8alkoxy, halogen-substituted C1-C8alkoxy or halogen. Preferred alkyl and alkoxy substituents are those containing 1 to 4 carbon atoms. Preferred substituents are C1-C4alkyl and halogen. R2 as naphthyl is preferably unsubstituted.
R2 as benzyl can be substituted by the substituents given for R2 as phenyl or naphthyl. Unsubstituted benzyl is preferred.
R2 as C1-C20alkyl is preferably C1-C8alkyl, especially C1-C6alkyl, and can be unsubstituted or substituted by, for example, C1-C8alkoxy, halogen, phenyl or naphthyl. Preferred are the unsubstituted alkyl groups, especially C1-C4alkyl.
Preferred groups R2 are C1-C6alkyl; halogen-substituted C1-C6alkyl; phenyl-substituted C1-C6alkyl; naphthyl-substituted C1-C6alkyl; phenyl which is unsubstituted or substituted by C1-C8alkyl, halogen-substituted C1-C8alkyl, C1-C8alkoxy-substituted C1-C8alkyl, C1C8alkoxy, halogen-substituted C1-C8alkoxy or halogen; naphthyl and benzyl which is substituted by C1-C4alkyl or halogen.
Highly preferred groups R2 are C1-C4alkyl; halogen-substituted C1-C4alkyl; phenyl which is unsubstituted or substituted by C1-C4alkyl or halogen; naphthyl and benzyl which is unsubstituted or substituted by C1-C4alkyl or halogen, especially phenyl which is unsubstituted or substituted by C1-C4alkyl.
Preferred are developers of formula (1), wherein.
R1 is phenyl which is substituted by C1-C4alkyl, preferably by methyl,
X is a group of the formula 
A is phenylene which is unsubstituted or substituted by C1-C8alkyl or halogen, preferably unsubstituted phenylene, like 1,3-phenylene,
B is a linking group of formula xe2x80x94Oxe2x80x94SO2xe2x80x94 or xe2x80x94Oxe2x80x94 and
R2 is phenyl, naphthyl or benzyl which is unsubstituted or substituted by C1-C4alkyl or halogen, especially phenyl which is substituted by C1-C4alkyl.
The compounds of formula (1) can be prepared in accordance with schemes 1-3 below; 
where R1, R2, A, B and X are as defined above and E is alkyl or aryl.
Furthermore, in the case where the species H2Nxe2x80x94Axe2x80x94Bxe2x80x94H is available the compounds of formula (1) can be prepared in accordance with scheme 4 below; 
In the case of schemes 1, 2 and 4 the R1-sulphonylisocyanate (or R1-sulphonamide) is reacted with R2-amine (or R2-isocyanate) in the presence or absence of an organic solvent. Preferably in the presence of an (apolar or polar) aprotic solvent such as aromatic hydrocarbons, chlorinated aromatic hydrocarbons, aliphatic or alicyclic hydrocarbons, chlorinated hydrocarbons, dialkylacylamides, aliphatic esters, aliphatic ketones, alicyclic ketones, aliphatic ethers, cyclic ethers, alkylnitriles and mixtures thereof. Most preferred are toluene, xylenes, petroleum ether, cyclohexane, dimethyl formamide, dimethylacetamide, ethylacetate, propyl acetate, butylacetate, diethylether, dibutylether, tetrahydrofuran, acetone, butanone, cyclohexanone, nitromethane, acetonitrile, propionitrile, nitromethane, ethyleneglycoldimethylether, chloroform, dichloromethane, carbon tetrachloride, chlorobenzene, dichlorobenzene, dioxan or mixtures thereof. Polar protic solvents such as alcohols may also be used. The reaction is preferably carried out at 0-100xc2x0 C. preferably 0-40xc2x0 C. for up to 12 hours. The reaction may further be catalysed by tertiary amines, carboxylic acids, amides or ureas.
In the case of scheme 3, the reaction of carbamate R1SO2NHCXOE with amine R2BANH2 may be carried out in excess amine, water, organic solvent or mixture thereof in the presence or absence of an inorganic or organic base. Typical solvents include those discussed hereinbefore. Bases used include alkali metal carbonates (K2CO3, Na2CO3), alkali metal hydroxides (NaOH, KOH), alkali metal alkoxides (sodium methoxide), pyridine, tertiary amines such as triethylamine, diisopropylethylamine.
Many syntheses are known for sulphonyl ureas and are incorporated herein by reference (J.Med.Chem., 1990, (33), 9, 2393, Chem.Rev., 1952, (50), 1, Chem.Rev., 1965, (65), 365).
In addition, the present invention is directed to novel compounds of formula 
wherein
R1 is unsubstituted or substituted phenyl, naphthyl or C1-C20alkyl,
R3 and R4 independently of each other are hydrogen, C1-C8alkyl, halogen-substituted
C1-C8alkyl, C1-C8alkoxy-substituted C1-C8alkyl, C1-C8alkoxy, halogen-substituted C1-C8alkoxy, C1-C8alkylsulphonyl, halogen, phenyl, phenoxy or phenoxycarbonyl,
X is a group of the formula 
B is a linking group of formula xe2x80x94Oxe2x80x94SO2xe2x80x94, xe2x80x94SO2xe2x80x94Oxe2x80x94, xe2x80x94SO2xe2x80x94NHxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94, xe2x80x94COxe2x80x94NHxe2x80x94SO2xe2x80x94, xe2x80x94SO2xe2x80x94NHxe2x80x94COxe2x80x94, xe2x80x94Oxe2x80x94COxe2x80x94Oxe2x80x94 or xe2x80x94Oxe2x80x94POxe2x80x94(OR2)2 and R2 is unsubstituted or substituted phenyl, naphthyl or C1-C20alkyl, with the proviso, that, if B is not a linking group of formula xe2x80x94Oxe2x80x94SO2xe2x80x94, R2 is unsubstituted or substituted phenyl, naphthyl or C1-C8alkyl.
As to R1, R2, X and B the above preferences apply.
Preferably, R3 and R4 are hydrogen, C1-C8alkyl, halogen-substituted C1-C8alkyl, C1-C8alkylsulphonyl or halogen. Preferred alkyl and alkoxy groups R3 and R4 contain 1 to 4 carbon atoms. Highly preferred groups R3 and R4 are hydrogen, C1-C4alkyl or halogen, especially hydrogen.
Of importance are compounds of formula (2), wherein
R1 is phenyl which is substituted by C1-C4alkyl, preferably by methyl,
X is a group of the formula 
R3 and R4 independently of each other are hydrogen, C1-C4alkyl or halogen, preferably hydrogen,
B is a linking group of formula xe2x80x94Oxe2x80x94SO2xe2x80x94, and
R2 is phenyl which is unsubstituted or substituted by C1-C4alkyl, especially phenyl which is substituted by C1-C4alkyl.
The compounds of formula (2) can be prepared as given above for the compounds of formula (1).
The colour forming compounds are, for example, triphenylmethanes, lactones, benzoxazines, spiropyrans or preferably fluorans.
Preferred colour formers include but are not limited to; 3-diethylamino-6-methylfluoran, 3-dimethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-(2,4-dimethylanilino) fluoran, 3-diethylamino-6-methyl-7-chlorofluoran, 3-diethylamino-6-methyl-7-(3-trifluoromethylanilino) fluoran, 3-diethylamino-6-methyl-7-(2-chloroanilino)fluoran, 3-diethylamino-6-methyl-7-(4-chloroanilino) fluoran, 3-diethylamino-6-methyl-7-(2-fluoroanilino) fluoran, 3-diethylamino-6-methyl-7-(4-n-octylanilino) fluoran, 3-diethylamino-7-(4-n-octylanilino)fluoran, 3-diethylamino -7-(n-octylamino)fluoran, 3-diethylamino-7-(dibenzylamino)fluoran, 3-diethylamino-6-methyl-7-(dibenzylamino) fluoran, 3-diethylamino-6-chloro-7-methylfluoran, 3-diethylamino-7-t-butylfluoran, 3-diethylamino-7-carboxyethylfluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3-diethylamino-6-methyl-7-(3-methylanilino)fluoran, 3-diethylamino-6-methyl-7-(4-methylanilino)fluoran, 3-diethylamino-6-ethoxyethyl-7-anilinofluoran, 3-diethylamino-7-methylfluoran, 3-diethylamino-7-chlorofluoran, 3-diethylamino-7-(3-trifiuoromethylanilino)fluoran, 3-diethylamino-7-(2-chloroanilino)fluoran, 3-diethylamino-7-(2-fluoroanilino)fluoran, 3-diethylamino-benzo[a]fluoran, 3-diethylamino-benzo[c]fluoran, 3-dibutylamino-7-dibenzylaminofluoran, 3-dibutylamino-7-anilinofluoran, 3-diethyiamino-7-anilinofluoran, 3-dibutylamino-6-methylfluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7-(2,4-dimethylanilino)fluoran, 3-dibutytamino-6-methyl-7-(2-chloroanilino)fluoran, 3-dibutylamino-6-methyl-7-(4-chloroanilino)fluoran, 3-dibutylamino-6-methyl-7-(2-fluoroanitino)fluoran, 3-dibutylamino-6-methyl-7-(3-trifluoromethylanilino)fluoran, 3-dibutylamino-6-ethoxyethyl-7-anilinofluoran, 3-dibutylamino-6-chloro-anilinofluoran, 3-dibutylamino-6-methyl-7-(4-methylanilino)fluoran, 3-dibutylamino-7-(2-chloroanilino)fluoran, 3-dibutylamino-7-(2-fluoroanilino)fluoran, 3-dibutylamino-7-(N-methyl-N-formylamino)fluoran, 3-dipentylamino-6-methyl-7-anilinofluoran, 3-dipentylamino-6-methyl-7-(4-2-chloroanilino)fluoran, 3-dipentylamino-7-(3-trifluoromethylanilino)fluoran, 3-dipentylamino-6-chloro-7-anilinofluoran, 3-dipentylamino-7-(4-chloroanilino)fluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-propylamino)-6-methyl-7-anilinoftuoran, 3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-p-toluidino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamylamino)-6-chloro-7-anilinofluoran, 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isobutylamino)-6-methyl-7-anilinofluoran, 3-(N-butyl-N-isoamylamino)-6-methyl-7-anilinofluoran, 3-(N-isopropyl-N-3-pentylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-ethoxypropylamino)-6-methyl-7-anilinofluoran, 3-cyclohexylamino-6-chlorofluoran, 2-methyl-6-p-(p-dimethytaminophenyl)aminoanilinofluoran, 2-methoxy-6-p-(p-dimethylaminophenyl)aminoanilinofluoran, 2-chloro-3-methyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran, 2-diethylamino-6-p-(p-dimethylaminophenyl)aminoanilinofluoran, 2-phenyl-6-methyl-6-p-(p-phenytaminophenyl)aminoanilinofluoran, 2-benzyl-6-p-(p-phenylaminophenyl)aminoanilinofluoran, 3-methyl-6-p-(p-dimethylaminophenyl)amino-anilinofluoran, 3-diethylamino-6-p-(p-diethylaminophenyl)aminoanilinofluoran, 3-diethyl-amino-6-p-(p-dibutylaminophenyl)aminoanilinofluoran, 2,4-dimethyl-6-[(4-dimethylamino)-anilino]fluoran, 3-[(4-dimethylaminophenyl)amino]-5,7-dimethylfluoran, 3,6,6xe2x80x2-tris(dimethyl-amino)spiro[fluorene-9,3xe2x80x2-phthalide], 3,6,6xe2x80x2-tris(diethylamino)spiro[fluorene-9,3xe2x80x2-phthalide], 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide, 3,3-bis(p-dimethylamino-phenyl)phthalide, 3,3-bis-[2-(p-dimethyiaminophenyl)-2-(p-methoxyphenyl)ethenyl-4,5,6,7-tetrabromophthalide, 3,3-bis-[2-(p-dimethylaminophenyl)-2-(p-methoxyphenyl)ethenyl-4,5,6,7-tetrachlorophthalide, 3,3-bis[1,1-bis(4-pyrrolidinophenyl)ethylene-2-yl]-4,5,6,7-tetrabromophthalide, 3,3-bis-(1-(4-methoxyphenyl)-1-(4-pyrridinophenyl)ethylene-2-yl]-4,5,6,7-tetrachlorophthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-ethyl-2-methylindole-3-yl)-4-azaphthalide, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-octyl-2-methylindole-3-yl)-4-azaphthalide, 3-(4-cyclohexylethylamino-2-methoxyphenyl)-3-(1-ethyl-2-methylindole-3-yl)-4-azaphthalide, 3,3-bis(1-ethyl-2-methylindole-3-yl)phthalide, 3,3-bis(1-octyl-2-methylindole-3-yl)phthalide, mixture of 2-phenyl-4-(4-diethylaminophenyl)-4-(4-methoxyphenyl)-6-methyl-7-dimethylamino-3,1-benzoxazine and 2-phenyl-4-(4-diethylaminophenyl)-4-(4-methoxyphenyl)-8-methyl-7-dimethylamino-3,1-benzoxazine, 4,4xe2x80x2-[1-methylethylidene)-bis(4,1-phenyleneoxy-4,2-quinazolinediyl)]bis[N,N-diethylbenzenamine], bis(N-methyldiphenylamine)-4-yl-(N-butylcarbazole)-3-yl-methane and mixtures thereof.
All of the above colour forming compounds can be used singly or as a mixture with other colour forming compounds; or they may also be used together with further black colour forming compounds.
Highly preferred are 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-(3-methylanilino)fluoran, 3-diethylamino-6-methyl-7-(2,4-dimethylanilino)fluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3-dipentylamino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-propylamino)-6-methyl-7-anilinofluoran, 3-(N-methyl-N-cyclohexylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran, 3-diethylamino-6-chloro-7-anilinofluoran, 3-dibutylamino-7-(2-chloroanilino)fluoran, 3-N-ethyl-p-toluidino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isobutylamino)-6-methyl-7-anilinofluoran, 3-N-ethyl-N-ethoxypropylamino-6-methyl-7-anilinofluoran, 2,4-dimethyl-6-[(4-dimethylamino)anilino]fluoran, 3-(4-diethylamino-2-ethoxyphenyl)-3-(1-octyl-2-methylindole-3yl)-4-azaphthalide, 3,3-bis(pdimethylamino-phenyl)-6-dimethytaminophthalide and mixtures thereof.
It is also possible to use solid solutions comprising at least two colour forming compounds.
A monophase (or single-phase or guest-host) solid solution possesses a crystal lattice which is identical with the crystal lattice of one of its components. One component is embedded as the xe2x80x98guestxe2x80x99 in the crystal lattice of the other component, which acts as the xe2x80x98hostxe2x80x99. The X-ray diffraction pattern of such a monophase solid solution is substantially identical to that of one of the components, called the xe2x80x98hostxe2x80x99. Within certain limits, different proportions of the components produce almost identical results.
In the literature, the definitions by the various authors, such as, G. H. Van""t Hoff, A. I. Kitaigorodsky and A. Whitacker for solid solutions and mixed crystals are often contradictory, (cf, e.g. xe2x80x98Analytical Chemistry of Synthetic Dyesxe2x80x99, Chapter 10/page 269, Editor K. Venkataraman, J. Wiley, New York, 1977).
The term xe2x80x98monophase solid solutionxe2x80x99 or xe2x80x98multiphase solid solutionxe2x80x99 or mixed crystalxe2x80x99, as defined herein, therefore, should be taken from the following definitions, which have been adapted to the current improved state of knowledge of such systems:
A monophase (or single-phase or guest-host) solid solution possesses a crystal lattice which is identical with the crystal lattice of one of its components. One component is embedded as the xe2x80x98guestxe2x80x99 in the crystal lattice of the other component, which acts as the xe2x80x98hostxe2x80x99. The X-ray diffraction pattern of such a monophase solid solution is substantially identical to that of one of the components, called the xe2x80x98hostxe2x80x99. Within certain limits, different proportions of the components produce almost identical results.
A multiphase solid solution possesses no precise, uniform crystal lattice. It differs from a physical mixture of its components in that the crystal lattice of at least one of its components is partially or competely altered. In comparison to a physical mixture of the components, which gives an X-ray diffraction diagram that is additive of the diagrams seen for the individual components. The signals in the X-ray diffraction diagram of a multiphase solid solution are broadened, shifted or altered in intensity. In general, different proportions of the components produce different results.
A mixed crystal (or solid compound type) solid solution possesses a precise composition and a uniform crystal lattice, which is different from the crystal lattices of all its components. If different proportions of the components lead, within certain limits, to the same result, then a solid solution is present in which the mixed crystal acts as a host.
For the avoidance of doubt it may also be pointed out that, inter alia, there may also be amorphous structures and mixed aggregates consisting of different particles of different physical type, such as, for example, an aggregate of different components each in pure crystal modification. Such amorphous structures and mixed aggregates cannot be equated with either solid solutions or mixed crystals, and possess different fundamental properties.
As hereinbefore detailed, the monophase solid solutions comprise a plurality of colour compounds. Suitable colour forming materials which may be included in the solid solutions are those given above.
Of particular interest are the following monophase solid solutions:
3-dibutylamino-6-methyl-7-anilinofluoran and 3-dibutylamino-7-dibenzylaminofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-dibutylamino-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-diethylamino-7-anilinofluoran;
3-diethylamino-6-methyl-7-anilinofluoran and 3-diethylamino-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-diethylamino-6-methyl-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-N-isoamyl-N-ethylamino-6-methy l-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-N-2-pentyl-N-ethylamino-6-methyl-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-N-isopropyl-N-ethylamino-6-methyl-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-N-Cyclohexylmethyl-N-ethylamino-6-methyl-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-dipropylamino-6-methyl-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-N-2-butyl-N-ethylamino-6-methyl-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-N-cyclohexyl-N-methylamino-6-methyl-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-diethylamino-6-methyl-7-(3-methylanilino) fluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-diethylamino-6-methyl-7-(2,4-dimethylanilino)fluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-dipentylamino-6-methyl-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-(N-methyl-N-propylamino)-6-methyl-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-diethylamino-6-chloro-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-dibutylamino-7-(2-chloroanilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-N-ethyl-p-toluidino-6-methyl-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3-(N-ethyl-N-isobutylamino)-6-methyl-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anifinofluoran and 3-N-ethyl-N-ethoxypropylamino-6-methyl-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 2,4-dimethyl-6-[(4-dimethylamino)anilino]fluoran
3-N-isoamyl-N-ethylamino-6-methyl-7-anilinofluoran and 3-diethylamino-6-methyl-7-anilinofluoran;
3-diethylamino-6-methyl-7-anilinofluoran and 3-N-propyl-N-methylamino-6-methyl-7-anifinofluoran;
3-diethylamino-6-methyl-7-(3-tolyl)aminofluoran and 3-diethylamino-6-methyl-7-anilinofluoran;
3-dibutylamino-6-methyl-7-anilinofluoran and 3,3-bis(1-octyl-2-methylindol-3-yl)phthalide;
3-dibutylamino-6-methyl-7-anilinofluoran and mixture of 2-phenyl-4-(4-diethylaminophenyl)-4-(4-methoxyphenyl)-6-methyl-7-dimethylamino-3,1-benzoxazine and 2-phenyl-4-(4-diethylaminophenyl)-4-(4-methoxyphenyl)-8-methyl-7-dimethylamino-3,1-benzoxazine;
3-dibutylamino-6-methyl-7-anilinofluoran and 4,4xe2x80x2-[1-methylethylidene)bis(4,1-phenyleneoxy-4,2-quinazolinediyl)]bis[N,N-diethylbenzenamine].
In the above monophase solid solutions the first compound is in a molar ratio of 75 to 99.9% by mole, the second compound is in a ratio of 25 to 0.1% by mole.
Examples of monophase solid solutions comprising two components A and B in the stated ratios are: 3-dibutylamino-6-methyl-7-anilinofluoran (99.9%), 3-diethylamino-6-methyl-7-anilinofluoran (0.1%);
3-dibutylamino-6-methyl-7-anilinofluoran (99%), 3-diethylamino-6-methyl-7-anilinofluoran (1%);
3-dibutylamino-6-methyl-7-anilinofluoran (95%), 3-diethylamino-6-methyl-7-anilinofluoran (5%);
3-dibutylamino-6-methyl-7-anilinofluoran (90%) and 3-N-2-pentyl-N-ethylamino-6-methyl-7anilinofluoran (10%);
3-dibutylamino-6-methyl-7-anilinofluoran (95%) and 3-N-2-pentyl-N-ethylamino-6-methyl-7-anilinofluoran (5%);
3-dibutylamino-6-methyl-7-anilinofluoran (90%) and 3-N-isopropyl-N-ethylamino-6-methyl-7-anilinoftuoran (10%);
3-dibutylamino-6-methyl-7-anilinofluoran (95%) and 3-N-isopropyl-N-ethylamino-6-methyl-7-anilinofluoran (5%);
3-dibutylamino-6-methyl-7-anilinofluoran (90%) and 3-N-Cyclohexylmethyl-N-ethylamino-6-methyl-7-anilinofluoran (10%);
3-dibutylamino-6-methyl-7-anilinofluoran (95%) and 3-N-Cyclohexylmethyl-N-ethylamino-6-methyl-7-anilinofluoran (5%);
3-dibutylamino-6-methyl-7-anilinofluoran (90%) and 3-dipropylamino-6-methyl-7-anilinofluoran (10%);
3-dibutylamino-6-enethyl-7-anilinofluoran (95%) and 3-dipropylamino-6-methyl-7-anilinofluoran (5%);
3-dibutylamino-6-methyl-7-anilinofluoran (90%) and 3-N-2-butyl-N-ethylamino-6-methyl-7-anilinofluoran (10%);
3-dibutylamino-6-methyl-7-anilinofluoran (95%) and 3-N-2-butyl-N-ethylamino-6-methyl-7-anilinofluoran (5%);
3-dibutylamino-6-methyl-7-anilinofluoran (90%), 3-diethylamino-6-methyl-7-anilinofluoran (10%);
3-dibutyfamino-6-methyl-7-anilinofluoran (85%), 3-diethyiamino-6-methyl-7-anilinofluoran (15%);
3-dibutylamino-6-methyl-7-anilinofluoran (80%), 3-diethylamino-6-methyl-7-anilinofluoran (20%);
3-dibutylamino-6-methyl-7-anifinofluoran (95%), 3-N-isoamyl-N-ethylamino-6-methyl-7-anilinofluoran (5%);
3-dibutylamino-6-methyl-7-anilinofluoran (90%), 3-N-isoamyl-N-ethylamino-6-methyl-7-anilinofluoran (10%);
3-dibutylamino-6-methyl-7-anilinofluoran (80%), 3-N-isoamyl-N-ethylamino-6-methyl-7-anilinofluoran (20%);
3-dibutylamino-6-methyl-7-anilinofluoran (90%), 3-N-cyclohexyl-N-methylamino-6-methyl-7-anilinofluoran (10%);
3-diethylamino-6-methyl-7-anilinofluoran (90%), 3-N-isoamyl-N-ethylamino-6-methyl-7-anilinofluoran (10%);
3-diethylamino-6-methyl-7-anilinofluoran (80%), 3-N-isoamyl-N-ethylamino-6-methyl-7-anilinofluoran (20%);
3-diethylamino-6-methyl-7-anilinofluoran (20%), 3-N-isoamyl-N-ethylamino-6-methyl-7-anifinofluoran (80%);
3-diethyiamino-6-methyl-7-anilinofluoran (10%), 3-N-isoamyl-N-ethylamino-6-methyl-7-anilinofluoran (90%);
3-diethyiamino-6-methyl-7-anilinofluoran (90%), 3-N-propyl-N-methylamino-6-methyl-7-anilinofluoran (10%);
3-diethylamino-6-methyl-7-anilinofluoran (80%), 3-N-propyl-N-methylamino-6-methyl-7-anilinofluoran (20%);
3-diethylamino-6-methyl-7-anilinofluoran (20%), 3-N-propyl-N-methylamino-6-methyl-7-anilinofluoran (80%);
3-diethylamino-6-methyl-7-anilinofluoran (10%), 3-N-propyl-N-methylamino-6-methyl-7-anilinofluoran (90%);
3-diethylamino-6-methyl-7-anilinofluoran (10%), 3-diethylamino-6-methyl-7-(3-tolyl)aminofluoran (90%);
3-diethylamino-6-methyl-7-anilinofluoran (20%), 3-diethylamino-6-methyl-7-(3-tolyl)aminofluoran (80%);
3-dibutylamino-6-methyl-7-anilinofluoran (90%), 3,3-bis(1-octyl-2-methylindol-3-yl)phthalide (10%);
3-diethyiamino-6-methyl-7-anilinofluoran (80%), 3,3-bis(1-octyl-2-methylindol-3-yl)phthalide(20%);
3-dibutylamino-6-methyl-7-anilinofluoran (90%), mixture of 2-phenyl-4-(4-diethylaminophenyl)-4-(4-methoxyphenyl)-6-methyl-7-dimethylamino-3,1-benzoxazine and 2-phenyl-4-(4-diethylaminophenyl)4-(4-methoxyphenyl)-8-methyl-7-dimethylamino-3,1-benzoxazine(10%);
3-dibutylamino-6-methyl-7-anifinofluoran (80%), mixture of 2-phenyl-4-(4-diethylaminophenyl)-4-(4-methoxyphenyl)-6-methyl-7-dimethylamino-3,1-benzoxazine and 2-phenyl-4-(4-diethylaminophenyl)-4-(4-methoxyphenyl)-8-methyl-7dimethylamino-3,1-benzoxazine(20%);
3-dibutylamino-6-methyl-7-anilinofluoran (90%), 4,4xe2x80x2-[1-methylethylidene)bis(4,1-phenyleneoxy-4,2-quinazolinediyl)bis(N,N-diethylbenzenamine](10%);
3-dibutylamino-6-methyl-7-anilinofluoran (80%), 4,4xe2x80x2-[1-methylethylidene)bis(4,1-phenyleneoxy-4,2-quinazolinediyl)]bis[N,N-diethylbenzenamine] (20%).
The monophase solid solutions can be used singly or as a mixture with other colour forming compounds such as triphenylmethanes, lactones, fluorans, benzoxazines and spiropyrans; or they may also be used together with further black colour forming compounds. Examples of such other colour forming compounds are given hereinbefore.
The monophase solid solutions can be prepared by a variety of methods. One such method is the recrystallisation method wherein a physical mixture of the desired components is dissolved, with or without heating, in a suitable solvent or solvent mixture. Suitable solvents include but are not limited to toluene, benzene, xylene, dichlorobenzene, chlorobenzene, 1,2-dichloroethane, methanol, ethanol, iso-propanol, n-butanol, acetonitrile, dimethylformamide or mixtures of these solvents with each other and with water. The monophase solid solution is then isolated by crystallisation from the solvent or solvent mixture. This can be brought about by cooling, standing, addition of a further solvent to promote crystallisation or concentration by standard means such as distillation, steam distillation and vacuum distillation. When the monophase solid solution is isolated by concentration it may be advantageous to do so in the presence of a small amount of base, to improve the visual aspect of the isolated product.
Alternatively, monophase solid solutions can be prepared from mixtures of the appropriate starting materials. The technique can be used to produce mixtures of two or more fluorans or phthalides. For example, mixtures of two fluorans are produced by replacing a single starting material with two analogous materials to the same total molar concentration in the reaction. In the case of fluorans, these starting materials are derivatives of amino phenols, phthalic anhydrides, keto acids and diphenylamines.
In addition, the heat sensitive recording material can contain a previously known developer, unless the colour forming performance of the resultant heat sensitive material is disturbed thereby. Such developers are exemplifed by but not limited to; 4,4xe2x80x2-isopropylidene bisphenol, 4,4xe2x80x2-sec-butylidene bisphenol, 4,4xe2x80x2-cyclohexylidene bisphenol, 2,2-bis-(4-hydroxyphenyl)-4-methylpentane, 2,2-dimethyl-3,3-di(4-hydroxyphenyl)butane, 2,2xe2x80x2-dihydroxydiphenyl, 1-phenyl-1,1-bis(4-hydroxyphenyl)butane, 4-phenyl-2,2-bis(4-hydroxyphenyl)butane, 1-phenyl-2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4xe2x80x2-hydroxy-3xe2x80x2-methylphenyl)-4-methylpentane, 2,2-bis(4xe2x80x2-hydroxy-3xe2x80x2-tert-butyllphenyl)-4-methylpentane, 4,4xe2x80x2-sec-butylidene-bis (2-methylphenol), 4,4xe2x80x2-isopropylidene-bis (2-tert-butylphenol), 2,2-bis(4xe2x80x2-hydroxy-3xe2x80x2-isopropylphenyl)-4-methylpentane, allyl-4,4-bis (4xe2x80x2-hydroxyphenyl) pentanoate, propargyl-4,4-bis(4xe2x80x2-hydroxyphenyl)pentanoate, n-propyl-4,4-bis (4xe2x80x2-hydroxyphenyl)pentanoate, 2,4-bis (phenylsulfonyl)phenol, 2-(4-methylsulfonyl)-4-(phenylsulfonyl)phenol, 2-(phenylsulfonyl)-4-(4-methylsulfonyl)phenol, 2,4-bis (4-methylphenylsulfonyl)phenol, pentamethylene-bis(4-hydroxybenzoate), 2,2-dimethyl-3,3-di(4-hydroxyphenyl)pentane, 2,2-di(4-hydroxyphenyl)hexane, 4,4xe2x80x2-dihydroxydiphenyl thioether, 1,7-di(4-hydroxyphenylthio)-3,5-dioxaheptane, 2,2xe2x80x2-bis(4-hydroxyphenylthio)diethyl ether, 4,4xe2x80x2-dihydroxy-3,3xe2x80x2-dimethylphenyl thioether; benzyl-4-hydroxybenzoate, ethyl-4-hydroxybenzoate, propyl-4-hydroxybenzoate, isopropyl-4-hydroxybenzoate, butyl-4-hydroxybenzoate, isobutyl-4-hydroxybenzoate, 4,4xe2x80x2-dihydroxydiphenylsulfone, 2,4xe2x80x2-dihydroxydiphenyl sulfone, 4-hydroxy-4xe2x80x2-methyldiphenyl sulfone, 4-hydroxy-4xe2x80x2-isopropoxydiphenyl sulfone, 4-hydroxy-4xe2x80x2-butoxydiphenyl suffone, 4,4xe2x80x2-dihydroxy-3,3xe2x80x2-diallyldiphenyl sulfone, 3,4-dihydroxy-4xe2x80x2-methyldiphenyl sulfone, 4,4xe2x80x2-dihydroxy-3,3xe2x80x2,5,5xe2x80x2-tetrabromodiphenyl sulfone, 4,4xe2x80x2-bis (p-toluenesulphonylaminocarbonylamino) diphenyimethane, N-p-toluenesulphonyl-Nxe2x80x2-phenyl urea, dimethyl 4-hydroxyphthalate, dicyclohexyl 4-hydroxyphthalate, diphenyl 4-hydroxyphthalate, 4-[2-(4-methoxyphenyloxy)ethyloxy] salicylate, 3,5-di-tert-butylsalicylic acid, 3-benzyl salicylic acid, 3-(xcex1-methylbenzyl) salicylic acid, 3-phenyl-5-(xcex1,xcex1-dimethylbenzyl) salicylic acid, 3,5-di-xcex1-methylbenzyl salicylic acid; metal salts of salicylic acid, 2-benzylsulfonylbenzoic acid, 3-cyclohexyl-4-hydroxybenzoic acid, zinc benzoate, zinc 4-nitrobenzoate, 4-(4xe2x80x2-phenoxybutoxy)phthalic acid, 4-(2xe2x80x2-phenoxyethoxy)phthalic acid, 4-(3xe2x80x2-phenylpropyloxyyphthalic acid, mono (2-hydroxyethyl)-5-nitro-isophthalic acid, 5-benzyloxycarbonyl isophthalic acid, 5-(1xe2x80x2-phenylethanesulfonyl)isophthalic acid, bis(1,2-dihydro-1,5-dimethyl-2-phenyl-3H-pyrazol-3-one-O)bis(thiocyanato-N)zinc and mixtures thereof.
In addition, the heat sensitive recording material of the invention can contain a sensitiser.
Representative examples of sensitiser are stearamide, methylol stearamide, p-benzylbiphenyl, m-terphenyl, 2-benzyloxynaphthalene, 4-methoxybiphenyl, dibenzyl oxalate, di(4-methylbenzyl)oxalate, di(4-chlorobenzyl)oxalate, dimethyl phthalate, dibenzyl terephthalate, dibenzyl isophthalate, 1,2-diphenoxyethane, 1,2-bis(4-methylphenoxy)ethane, 1,2-bis(3-methylphenoxy)ethane, 4,4xe2x80x2-dimethylbiphenyl, phenyl-1-hydroxy-2-naphthoate, 4-methylphenyl biphenyl ether, 1,2-bis(3,4-dimethylphenyl)ethane, 2,3,5,6-4xe2x80x2-methyldiphenyl methane, 1,4-diethoxynaphthalene, 1,4-diacetoxybenzene, 1,4-diproprionoxybenzene, o-xylylene-bis(phenyl ether), 4-(m-methylphenoxymethyl) biphenyl, p-hydroxyacetanilide, p-hydroxybutyranilide, p-hydroxynonananilide, p-hydroxylauranilide, p-hydroxyoctadecan-anilide, N-phenyl-phenylsulphonamide and sensitisers of the formula 
wherein R and Rxe2x80x2 are identical or different from each other and each represent C1-C6alkyl.
Examples of R and Rxe2x80x2 are methyl, ethyl, n- or iso-propyl and n-, sec- or tert-butyl.
The substituents R and Rxe2x80x2 are identical or different from each other and each are preferably C1-C4alkyl, especially methyl or ethyl, in particular ethyl.
The above sensitisers are known or can be prepared according to known methods.
In addition, the heat sensitive recording material of the invention can contain a stabiliser.
Representative stabilisers for use in heat sensitive recording materials include 2,2xe2x80x2-methylene-bis(4-methyl-6-tert-butylphenol), 2,2xe2x80x2-methylene-bis(4-ethyl-6-tert-butylphenol), 4,4xe2x80x2-butylidene-bis(3-methyl-6-tert-butylphenol), 4,4xe2x80x2-thio-bis(2-tert-butyl-5-methylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, bis (3-tert-butyl-4-hydroxy-6-methylphenyl)sulfone, bis (3,5-dibromo-4-hydroxyphenyl)sulfone, 4,4xe2x80x2-sulfinyl bis (2-tert-butyl-5-methylphenol), 2,2xe2x80x2-methylene bis (4,6-di-tert-butylphenyl)phosphate and alkali metal, ammonium and polyvalent metal salts thereof, 4-benzyloxy-4xe2x80x2-(2-methylglycidyloxy)diphenyl sulfone, 4,4xe2x80x2-diglycidyloxydiphenyl sulfone,1,4-diglycidyloxybenzene, 4-[a-(hydroxymethyl)benzyloxy]4-hydroxydiphenyl sulfone, metal salts of p-nitrobenzoic acid, metal salts of phthalic acid mono benzyl ester, metal salts of cinnamic acid and mixtures thereof.
Preferred stabilisers are 4,4xe2x80x2-butylidene-bis(3-methyl-6-tert-butylphenol), 4,4xe2x80x2-thio-bis(2-tert-butyl-5-methylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 1,1,3-tris(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, 4-benzyloxy-4xe2x80x2-(2-methylglycidyloxy)diphenyl sulfone and mixtures thereof.
The heat sensitive recording material of the invention can be prepared according to conventional methods. For example, at least one colour forming compound, at least one developer and, if desired, at least one sensitiser are pulverised separately in water or a suitable dispersing medium, such as aqueous polyvinyl alcohol, to form an aqueous or other dispersion. If desired a stabiliser is treated in the same manner. The fine particle dispersions thus obtained are combined and then mixed with conventional amounts of binder, filler and lubricant.
Representative binders used for the heat sensitive recording material include polyvinyl alcohol (fully and partially hydroiysed), carboxy, amide, sulfonic and butyral modified polyvinyl alcohols, derivatives of cellulose such as hydroxyethyl cellulose, methyl cellulose, ethyl cellulose, carboxymethyl cellulose and acetyl cellulose, copolymer of styrene-maleic anhydride, copolymer of styrene-butadiene, polyvinyl chloride, polyvinyl acetate, polyacrylamide, polyamide resin and mixtures thereof.
Exemplary fillers which can be used include calcium carbonate, kaolin, calcined kaolin, aluminium hydroxide, talc, titanium dioxide, zinc oxide, silica, polystyrene resin, urea-formaldehyde resin, hollow plastic pigment and mixtures thereof.
Representative lubricants for use in heat sensitive recording materials include dispersions or emulsions of stearamide, methylene bisstearamide, polyethylene, carnauba wax, paraffin wax, zinc stearate or calcium stearate and mixtures thereof.
Other additives can also be employed, if necessary. Such additives are for example fluorescent whitening agents and ultraviolet absorbers.
The coating composition so obtained can be applied to a suitable substrate such as paper, plastic sheet and resin coated paper, and used as the heat sensitive recording material. The system of the invention can be employed for other end use applications using colour forming materials, for example, a temperature indicating material.
The quantity of the coating is usually in the range of 2 to 10 g/m2, most often in the range 4 to 8 g/m2.
The recording material containing such a thermosensitive colouring layer can in addition contain a protective layer and, if desired, an undercoat layer. The undercoat layer may be interposed between the substrate and the thermosensitive colouring layer.
The protective layer usually comprises a water-soluble resin in order to protect the thermosensitive colouring layer. If desired, the protective layer may contain water-soluble resins in combination with water-insoluble resins.
As such resins conventional resins can be employed. Specific examples are: polyvinyl alcohol; starch and starch derivatives; cellulose derivatives such as methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose and ethylcellulose; sodium polyacrylate; polyvinyl pyrrolidone; polyacrylamide/acrylic acid ester copolymers; acrylamide/acrylic acid ester/methacrylic acid copolymers; alkali metal salts of styrene/maleic anhydride copolymers; alkali metal salts of isobutylene/maleic anhydride copolymers; polyacrylamide; sodium alginate; gelatin; casein; water-soluble polyesters and carboxyl-group-modified polyvinyl alcohols.
The protective layer may also contain a water-resisting agent such as a polyamide resin, melamine resin, formaldehyde, glyoxal or chromium alum.
Furthermore, the protective layer may contain fillers, such as finely-divided inorganic powders, e.g. of calcium carbonate, silica, zinc oxide, titanium oxide, aluminium hydroxide, zinc hydroxide, barium sulphate, clay, talc, surface-treated calcium or silica, or a finely-divided organic powder of, e.g., a urea-formaldehyde resin, a styrene/methacrylic acid copolymer or polystyrene.
The undercoat layer usually contains as its main components a binder resin and a filler.
Specific examples of binder resins for use in the undercoat layer are: polyvinyl alcohol; starch and starch derivatives; cellulose derivatives such as methoxycellulose, hydroxyethylcellulose, carboxymethylcellulose, methylcellulose and ethylcellulose; sodium polyacrylate; polyvinyl pyrrolidone; polyacrylamide/acrylic acid ester copolymers; acrylamide/acrylic acid ester/methacrylic acid copolymers; alkali metal salts of styrene/maleic anhydride copolymers; alkali metal salts of isobutylene/maleic anhydride copolymers; polyacrylamide; sodium alginate; gelatin; casein; water-soluble polymers such as water-soluble polyesters and carboxyl-group-modified polyvinyl alcohols; polyvinyl acetate; polyurethanes; styrene/butadiene copolymers; polyacrylic acid; polyacrylic acid esters; vinyl chloride/vinyl acetate copolymers; polybutylmethacrylate; ethylen/vinylacetate copolymers and styrene/butadiene acrylic derivative copolymers.
Specific examples of fillers for use in the undercoat layer are: finely-divided inorganic powders, e.g. of calcium carbonate, silica, zinc oxide, titanium oxide, aluminium hydroxide, zinc hydroxide, barium sulphate, clay, talc, surface-treated calcium, silica or calcined clay (eg Ansilex,Engelhard Corp.), and finely-divided organic powders of, e.g., urea-formaldehyde resins, styrene/methacrylic acid copolymers and polystyrene.
In addition, the undercoat layer may contain a water-resisting agent. Examples of such agents are given above.
In particular the invention provides exceptional resistance to plasticiser, oil and heat ageing whilst showing an improved background whiteness.